try opening the excel file that you get as export from your Web page and open it in Notepad.
When we write code to write the datagrid on the page as while making the content type as excel, it doesn't actually create an excel file but creates HTML tables from datagrid and opens them in a file which has extension of XLS (or at least that is what it did a while ago for my apps). But I am very sure the XLS/CVS file that you are getting from your Web page contains HTML table and see how the formatting tags (bold, bullets so on) are showing up. that might give you an idea what you can do to fix the problem. Hope this helps.
new to programming but getting ther